NdisInitializeNPagedLookasideList function

Description

The NdisInitializeNPagedLookasideList function initializes a lookaside list. After a successful initialization, nonpaged fixed-size blocks can be allocated from and freed to the lookaside list.

Parameters

Lookaside [in]

A pointer to an NPAGED_LOOKASIDE_LIST structure that contains the caller-supplied lookaside list head to be initialized. The structure must be 16-byte aligned on 64-bit platforms. The driver must provide a list head that is resident—that is, in nonpaged system space.

Allocate [in, optional]

A function entry point that is either NULL or specifies the entry point of a caller-supplied Allocate function that will allocate an entry of the size that is specified in the Size member whenever it is called. If Allocate is NULL, the NdisAllocateFromNPagedLookasideList function subsequently allocates entries on behalf of the caller. If the caller provides an Allocate function, it also must provide a Free function.

Free [in, optional]

A function entry point that is either NULL or specifies the entry point of a caller-supplied Free function that will free an entry of the size that is specified in the Size member whenever it is called. If Free is NULL, the NdisFreeToNPagedLookasideList function subsequently frees entries on behalf of the caller.

Flags [in]

Must be zero. This parameter is reserved.

Size [in]

The size, in bytes, of each entry to be subsequently allocated from the lookaside list.

Tag [in]

A caller-supplied pool tag for lookaside list entries. The Tag is a string of four characters that is delimited by single quote marks (for example, 'derF'). The characters are usually specified in reverse order so they are easier to read when dumping pool or tracking pool usage in the debugger.

Depth [in]

Must be zero. This parameter is also reserved.

Remarks

NdisInitializeNPagedLookasideList initializes the caller-supplied list head but allocates no memory for list entries. The initial entries are allocated on an as-needed basis either with calls to the NdisAllocateFromNPagedLookasideList function or by the driver-supplied Allocate callback function at the Allocate parameter. The list is populated as the driver frees entries back to the list with the NdisFreeToNPagedLookasideList function. Entries collect on the list until a system-determined but dynamically sized limit is reached. Then, any surplus entries in the lookaside list are returned to nonpaged pool, either by NdisFreeToNPagedLookasideList or with calls to the driver-supplied Free callback function at the Free parameter.

All entries in the lookaside list are of the same size, which is specified in the Size parameter. A lookaside list is particularly useful to drivers that must dynamically allocate and free fixed-size context areas in which to maintain run-time state about their outstanding I/O operations. For instance, connection-oriented NDIS drivers are likely to find lookaside lists particularly useful because such drivers usually maintain a dynamic set of context areas to track outgoing and incoming calls.

It is more efficient for a driver to allow the NdisAllocateFromNPagedLookasideList and NdisFreeToNPagedLookasideList functions to manage the allocation and deallocation of entries (see the ExAllocatePoolWithTag and ExFreePool functions). However, a driver that tracks state internally about its memory usage might supply Allocate and Free functions to NdisInitializeNPagedLookasideList.

Callers of NdisInitializeNPagedLookasideList must be running at IRQL <= DISPATCH_LEVEL, but are usually running at PASSIVE_LEVEL.

See also

ExAllocatePoolWithTag

ExFreePool

NPAGED_LOOKASIDE_LIST

NdisAllocateFromNPagedLookasideList

NdisDeleteNPagedLookasideList

NdisFreeToNPagedLookasideList